This section is from the book "Culinary Herbs", by M. G. Kains. Also available from Amazon: Culinary Herbs, Their Cultivation, Harvesting, Curing and Uses.
Division of the clumps of such herbs as mint is often practiced, a sharp spade or a lawn edger being used to cut the clump into pieces about 6 inches square. The squares are then placed in new quarters and packed firmly in place with soil. This method is, however, the least satisfactory of all mentioned, because it too frequently deprives the plants of a large amount of roots, thus impairs the growth, and during the first season or two may result in unsymmetrical clumps. If done in early spring before growth starts, least damage is done to the plants.
Holt's Mammoth and Common Sage About Half Natural Size
Artificial methods of propagation, especially those of cuttage and layerage, have the further advantage over propagation by means of seeds, in the perpetuation of desired characters of individual plants, one or more of which may appear in any plantation. These, particularly if more productive than the others, should always be utilized as stock, not merely because their progeny artificially obtained are likely to retain the character and thus probably increase the yield of the plantation, but principally because they may form the nucleus of a choice strain.
Except in the respects mentioned, these methods of propagation are not notably superior to propagation by means of good seed, which, by the way, is not overabundant. By the consumption of a little extra time, any desired number of plants may be obtained from seed. At any rate, seed is what one must start with in nearly every case.
Marker for Hotbeds and Cold Frames